The present invention relates generally to microstrip antennas, and more particularly to a single element patch microstrip antenna which is adapted for dual frequency operation.
Microstrip antennas are one of the most active research and development subjects today. These antennas are unique in many ways: extremely compact in structure, light in weight, easy to fabricate and to reproduce precisely (by printed circuit technique), capable to be integrated with other microwave devices and IC circuits, etc. However, they are narrow-banded, unless thick substrate is used. In spite of this restriction, they find more and more applications each day, particularly wherever space and weight are limited.
In many applications, it is not operation in a continuous wide-band, but, operation in two or more discrete bands that is required. In this case, a thin patch capable of operating in multiple bands is highly desirable, particularly for large array application where considerable saving in space, weight, material and cost can be achieved. For that goal, a few attempts have been made by using two or more patch antennas stacked on top of each other, or placed side by side, or using a complex matching network which takes as much space and weight, if not more, as the element itself. Obviously in all those designs, the advantage of compact structure is sacrificed.
The task of producing microstrip antennas capable of two or more bands of operation has been alleviated, to some degree, by the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 4,379,296, issued to Farrar et al on Apr. 5, 1983; PA1 U.S. Pat. No. 4,367,474, issued on Schaubert et al on Jan. 4, 1983; PA1 U.S. Pat. No. 4,386,357, issued to Patton on May 31, 1983; PA1 U.S. Pat. No. 4,040,060, issued to Kaloi on Aug. 2, 1977; PA1 U.S. Pat. No. Re. 29,296, issued to Krutsinger et al on July 5, 1977; PA1 U.S. Pat. No. 4,191,959, issued to Kerr on Mar. 4, 1980; PA1 U.S. Pat. No. 4,489,328, issued to Gears on Dec. 18, 1984; PA1 U.S. Pat. No. 4,130,822, issued to Gonroy on Dec. 19, 1978; PA1 U.S. Pat. No. 4,197,545, issued to Favaloro et al on Apr. 8, 1980; PA1 U.S. Pat. No. 4,242,685, issued to Sanford on Dec. 30, 1980; PA1 U.S. Pat. No. 3,757,344, issued to Pereda on Sept. 4, 1973; and PA1 U.S. Pat. No. 4,078,237, issued to Kaloi on Mar. 7, 1978.
U.S. Pat. Nos. 4,379,296; 4,367,474; 4,386,357; 4,040,060; and 4,078,237 disclose patch antennas which include shorting pins. U.S. Pat. Nos. Re. 29,246, 4,191,959; 4,489,328; 4,130,822; 4,197,545; 4,242,685; and 3,757,344 disclose patch antennas with slots therein.
From the foregoing discussion, it is apparent that recent work has been directed towards the need to develop a single element microstrip antenna capable of operating at two or more controllable frequencies. The present invention is directed towards satisfying that need.